Heating and Air Conditioning: Description and Operation

CIRCUIT OPERATION
The A/C compressor for the air conditioning system is belt driven by the engine through the A/C compressor clutch. The clutch allows the compressor to be disengaged when air conditioning is not required, and allows the air conditioning load to be removed from the engine when needed.

With the Ignition Switch in RUN, voltage is applied to the coil of the A/C Control Relay. The relay is always grounded by G200. With the contacts closed, voltage is applied to the Heater and A/C Control assembly from Fuse 12.

Operation of the compressor depends on the particular mode selected by the driver. When the Mode Selector is in MAX, NORM, BI-LEVEL or DEF, battery voltage is applied through the heater and A/C control assembly to the remaining circuits.

The path to the A/C Compressor relay is through the A/C low pressure cut-out switch and the A/C high pressure cut-out switch, which are both normally closed. The A/C low pressure cut-out switch opens if the refrigerant pressure is too low to operate the A/C compressor without possible damage to it. The A/C high pressure cut-out switch opens if refrigerant pressure becomes too high for normal operation.

When the relay is energized voltage from the A/C high pressure cut-out switch is applied to the A/C compressor clutch through the closed contacts of the A/C compressor relay.

The A/C compressor relay is operated by the ECM. When the ECM receives the A/C ON signal at terminal B8, it grounds terminal A4, energizing the relay. When the relay is energized, voltage is applied to the A/C compressor clutch through the contacts of the relay. If the ECM determines that the engine load should be reduced, such as during full throttle, the A/C compressor relay is de-energized (which removes voltage from the A/C compressor clutch), thus removing the air conditioning load from the engine.